1. Field of the Invention
The present invention relates to a multilayer type electrophotographic photoconductor and an image forming apparatus. In particular, it relates to a multilayer type electrophotographic photoconductor capable of restraining generation of the exposure memory and the photo memory by limiting the light absorption degree (light absorbance) of a predetermined wavelength in a photoconductive layer, and an image forming apparatus comprising such a multilayer type electrophotographic photoconductor.
2. Description of the Related Art
Conventionally, as an electrophotographic photoconductor used for an electrophotographic machine such as a copying machine and a laser printer, an inorganic photoconductor comprising a photoconductive layer made of an inorganic material such as amorphous silicon, and an organic photoconductor comprising a photoconductive layer containing a charge generating agent, a charge transporting agent, and a binder resin, are known.
Among these photoconductors, the organic photoconductor having the production convenience and additionally, the excellent freedom in the structure design owing to the variety of the selection range of the charge generating agent, the charge transporting agent, or the like, is widely used. Moreover, the organic photoconductor is roughly classified into a single layer type organic photoconductor and a multilayer type organic photoconductor in terms of the layer configuration. In particular, since the multilayer type organic photoconductor has the functions separated per each layer, it is advantageous in terms of the design easiness and the function control so that it is widely used recently.
However, since the multilayer type organic photoconductor contains the charge generating agent and the charge transporting agent in different layers, the charge transporting ability in the charge generating layer can easily be lowered so that a problem of the image characteristic deterioration due to the charge accumulation inside the layer is involved.
In particular, problems of generation of the so-called exposure memory of transferring the charge generated in the previous rounds and accumulated inside the charge generating layer to an image in the following rounds, or the so-called photo memory of the influence to the evenness of the initial charge caused by the charge generated by the external beam accumulated inside the charge generating layer have been observed.
Then, for solving these problems, a method for improving the charge characteristics by improving the charge transporting ability in the charge generating layer by containing an electron transferring agent in the charge generating layer in a positive charge type multilayer type electrophotographic photoconductor has been proposed.
More specifically, a multilayer type electrophotographic photoconductor containing the same binder resin in the charge generating layer and the charge transfer layer, and an accepter compound contained having the electron transporting ability in the charge generating layer and the charge transporting layer has been proposed (for example, see patent documents 1 and 2).                [Patent document 1] JPH07-199487A (claims)        [Patent document 2] JPH07-219251A (claims)        
However, although the multilayer type electrophotographic photoconductors disclosed in patent documents 1 and 2 improve the charge characteristics, depending on the photoconductor material to be used, the printing conditions, or the like, the charge is accumulated in the charge generating layer so that the charge characteristics may be lowered.
In particular, depending on the kind of the charge generating agent or the charge transporting agent, the charge transporting ability may not be sufficiently obtained, or on the contrary, due to the excessive sensitivity to the exposure light source, the exposure memory may be generated. Moreover, in the case of the exposure of the electrophotographic photoconductor to the external beam for a long time at the time of replacement, or the like, the photo memory is also generated so that the charge characteristics may be lowered.